1. Field of the Invention
The present invention relates to a multi-ply, heat-shrinkable film adapted for so-called "zero-loss cooking method" (to be described in detail hereinafter) and having excellent adhesion properties to cooked or processed meat products and to a cooked or processed meat product packaged therewith.
2. Description of Prior Art
"Zero-loss cooking method" having recently become widespread comprises the following steps.
1. Seasonings are added to raw meat, followed by well kneading the meat for infiltrating the meat with the seasonings.
2. After leaving the meat infiltrated with the seasonings for about one day, the meat is again well kneaded and placed in a heat-shrinkable packaging bag, followed by vacuum packaging.
3. This packaged product is closely packed in a metal mold, followed by closing the metal mold and applying a load through a spring.
4. The metal mold packed with the packaged product is heat-treated in a steam of 75.degree. to 80.degree. C. for about 6 hours.
At this stage, the packaging bag shrinks due to its heat-shrinking properties, thus a tightly packaged product being obtained.
5. After the thermal treatment, the metal mold packed with the packaged product is cooled. After cooling, the packaged product is taken out of the metal mold, then stored in a refrigerator for about 20 hours to obtain a final product.
The above-described method is called "zero-loss cooking method" since it enables one to thermally process packaged meat as such to obtain a processed meat package, involving absolutely no losses with respect to meat and packaging material.
As packaging materials for use in such "zero-loss cooking method", there have so far been used those materials which have conventionally been used for packaging raw meat and processed meat, such as a three-ply laminate tubing made of heat-shrinkable film [ethylene-vinyl acetate copolymer (outer side of the tubing)/polyvinylidene chloride resin/cross linked ethylene-vinyl acetate copolymer (inner side of the tubing)] based on technique described in Japanese Examined Patent Publication No. 58-43024 (corresponding to U.S. Pat. No. 3,741,253) and four-ply laminate tubing made of heat-shrinkable film [polyamide resin (outer surface of the tubing)/saponified product of ethylene-vinyl acetate copolymer/an adhesive resin/ethylene-vinyl acetate copolymer (inner surface of the tubing)] based on the technique described in Japanese Unexamined Patent Publication Nos. 58-14743 and 59-152853. However, these heat-shrinkable films show such a poor adhesion to processed meat products obtained according to the "zero-loss cooking method" that meat juice (drip) of the cooked and processed meat product oozes out on the surface and gathers there, which causes the problem that the packaged product appears aged and the problem of deteriorated preservability due to propagation of bacteria.
Additionally, Japanese Examined Patent Publication No. 1-18865 (corresponding to U.S. Pat. No. 4,409,286) describes to use an ethylene-ethyl acrylate-maleic anhydride copolymer as one ply of a multi-ply structure. However, this film is neither a heat-shrinkable film nor a film for use in "zero-loss cooking method".